1. Field of the Invention
The invention relates to a method for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line. The invention furthermore relates to a control device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line.
2. Related Art
The fact that pollutant emissions from a combustion engine can be reduced in an effective manner by catalytic aftertreatment of the exhaust gas with the aid of an exhaust gas aftertreatment system, e.g., one having an exhaust gas catalyst, is known from practical experience. However, it is an important precondition for this that the catalyst has reached its light off temperature. Below this light off temperature, the exhaust gas catalyst is ineffective or not very effective, and the reaction takes place only at insufficiently low conversion rates. Particularly in systems with exhaust turbocharging, the heatsink formed by the exhaust turbine means that reaching catalyst light off in an optimum manner for emissions is extremely important in avoiding high pollutant emissions. In the case of combustion engines of this kind, it is thus necessary to take precautions to ensure that the exhaust gas catalyst reaches its light off temperature as quickly as possible.
In order to raise the exhaust gas temperature to a light off temperature, one known practice is to adjust the injection parameters of the combustion engine in such a way, for example, that the adjusted injection parameters bring about an increase in the exhaust gas temperature. This can be achieved by retarding the start of injection, for example.
Other known measures require the adjustment of a throttle valve, the activation of a burner system additionally introduced into the exhaust line or the closure of an engine braking flap. The disadvantage with the abovementioned approaches is that additional components, e.g., a burner system, an engine braking flap, etc., have to be provided and disadvantages in terms of efficiency have to be accepted.
European Patent Application EP 1 431 529 A1, for example, discloses a method and a device for raising and/or lowering an exhaust gas temperature of a combustion engine having an exhaust gas aftertreatment device arranged in an exhaust line, wherein the exhaust gas temperature is raised or lowered by gas introduced into the exhaust line. The gas introduction device used for this purpose can be an inserted nozzle configured as an injector or a shut-off nozzle inserted in the exhaust line or an ejector pump. The disadvantage of this technique is that an additional introduction device is necessary.
A combustion engine having an exhaust gas aftertreatment device in the form of a particulate filter is furthermore known from DE 43 25 004 C2. In the case of this particulate filter, raising (or lowering) the exhaust gas temperature in order to control the burn off process in the particulate filter is achieved by throttling (or de-throttling) the exhaust gas flowing through the exhaust line. This is achieved by a flap in the filter housing, which is pivoted by a thermostatically controlled linkage. In addition, an electric heater is provided for the thermostat and the particulate filter. This system is of complex construction and requires a large number of specially manufactured components. Thus, the particulate filter material must have a precisely defined contour to allow the pivoting motion of the flap. Moreover, effective control is only possible in relation to the raising of the exhaust gas temperature.